In an aircraft, it is necessary to sound-insulate the cabin and the cockpit. To determine the quantity of sound insulation required to obtain good insulation, it is known to place a microphone on the skin of the aircraft and thus measure the noise received by the fuselage during a real or wind-tunnel flight. However, the measurements given by such a microphone are contaminated by the turbulence of the boundary layer, the intensity of which varies with the speed of the aircraft and as a function of the position of the microphone on the fuselage.